This disclosure relates to generator systems, and more particularly to variable-speed constant-frequency power control using a variable frequency generator.
To produce electric power, aircraft typically use generators coupled to engines located on the wings. Different types of generators have been used that have varying levels of complexity and output power characteristics. Aircraft engines are normally used over a wide range of operating conditions in the air, including takeoff, cruise, descent, and landing. This demands that the engines operate over a range of rotating speeds. Previous generators required constant speed inputs for producing power and use mechanisms including constant speed drives and integrated drive generators. Such devices include heavy hydro-mechanical devices that are coupled to an input shaft rotating at varying input speeds (indexed to the engine speed) and deliver power to an output shaft that rotates at a constant speed, despite the varying input. The heavy hydro-mechanical devices may add unwanted loads to the wings of the aircraft.
Engine coupled generators having speeds directly indexed to an engine operate over the same wide range of operating speeds as the engine. These types of generators are frequently called variable frequency generators (VFGs). It is typical for the requirements and design of wound field type electrical power generators to deliver the same output power, current, and voltage over the entire wide speed range of the input speed. In a constant frequency generation system that conditions power from a VFG, control electronics typically employ static switch timing. Tightly coupled control of the VFG with power conversion control may increase the risk of faults or component defects producing abnormally high generator output voltages and/or other performance issues.